Authors: Hanžek-Turnšek, Hana; Tomažič, Marjana ;Benussi, Matteo;Jančič, Matic ;Lazar, Bojan ;

Fisheries discards, disposed catch of unwanted species or sizes, pose a significant threat to marine ecosystems. While global and regional estimates are available, assessments of macrobenthic invertebrate discards in small-scale fisheries are scarce. In this study, we quantified discards and their taxonomic composition in small-scale bottom set net fisheries in the Northern Adriatic Sea. The total catch of single-layer gillnets and three-layer trammel nets was monitored by onboard observers during regular fishing operations in 2019 and 2020. Target catch and discarded vertebrate species were determined and weighed on board. A random quarter of disposed invertebrates was subsampled for detailed laboratory analysis. Preliminary analysis indicates an average discard rate of 75.4% (SD: ± 16.7%). Organisms belonging to the Porifera, Mollusca (Gastropoda, Bivalvia), Echinodermata, Chordata (Tunicata) and Arthropoda (Crustacea) have jointly contributed 98.3% (IQR: 97.4 – 99.1) of wet weight. We estimate that a median of 47.2 kg (IQR: 25.6 – 65.5) of discards are produced per gross revenue of 100€. Our results show that regional discard rates can be up to three times higher than global estimates and suggest that the small-scale fisheries impact on marine ecosystems may be underestimated.